The present invention relates generally to a chemical vapor deposition apparatus and process. More particularly, it relates to a chemical vapor deposition apparatus characterized by the selective formation of metal films on metal and semiconductor surfaces of a substrate, such as a patterned silicon wafer and a method for its use.
There is a continuous trend in the development of solid state circuitry to reduce the dimensions of devices in integrated circuits and in this way increase the speed of operation. As the dimensions of devices on substrates such as silicon wafers continues to shrink, the contact openings in insulating layers to conductors and semiconductors become smaller and the lateral dimensions of these openings approach the dimension normal to the surface, thus requiring steep sides for these openings to accommodate close packing and achieve the high density required. Coverage of the steep sides of the contact openings by the succeeding conductor becomes difficult and the recessed surface of these openings makes lithography for subsequent layers difficult.
The need is recognized for improvement in formation of conductive films in these close packed contact openings on silicon wafers. A solution to this problem will be to grow a metal selectively on the conductor and semiconductor surfaces by chemical vapor deposition. However, to deposit thick films of metals, one must use a reducing atmosphere, such as hydrogen, to react with the depositing gas. Selective deposition is difficult under these conditions. For example, to obtain tungsten films greater than 500 Angstroms thick, it is necessary to react tungsten hexafluoride with hydrogen. Selectivity is lost by such a reaction and tungsten growth on insulator surfaces occurs after about 1000 Angstroms of growth on the conductor surfaces, as disclosed by Saraswat et al, in Selective CVD of Tungsten for VLSI Technology, Stanford University, May 1984.
The selectivity of metal deposition is known to be dependent on the deposition process conditions including temperature, pressure and reactant concentration in addition to the composition of the substrate surface. These reaction variables can be controlled within conventional chemical vapor deposition reactors. The apparatus and process of this invention provide enhanced selectivity of metal deposition by controlling an additional variable, i.e., the radiation which impinges upon the depositing surfaces of the substrate.